Medical implant

ABSTRACT

Medical implant which at least partially comprises a biocompatible, electrically conductive polymer with electrical resistivity p, having the property of being able to be heated and softened by a flow of current through the polymer.

The invention refers to a medical implant according to the main conceptof patent claim 1, a device comprising a medical implant according tothe main concept of patent claim 70, an osteosynthesis process accordingto the main concept of patent claim 71 and a further osteosynthesisprocess according to the main concept of patent claim 81.

The use of biocompatible, thermoplastic materials for osteosynthesis andsimilar processes for fastening purposes on human or animal bones is aknown state of the art and has been attempted in various ways, forinstance by an external application of heat as in a hot gluing pistol(for instance U.S. Pat. No. 5,290,281), or by liquefying a polymer byultrasound wave energy according to WO2006/002569 WOODWELDING. Thesetechniques are however affected by disadvantages: the warming-up byexternal heat sources—as in a hot gluing pistol—means that an implantmust be inserted very quickly, so as not to cool off again whileundergoing the connection with the bones, because it typically presentsonly a small thermal capacity and the thermoplastic material can forinstance penetrate into the interspaces in the bone only in a softenedcondition. As soon as the material has cooled off, no further connectionwith the bone occurs. Even the necessary excessive warming-up of thethermoplastic materials—to prevent a premature solidification—isdisadvantageous, because it causes damage to both the material and the(bone) tissue. Moreover, the heating—as would ideally be desirable—doesnot merely heat-up the transition zone to the tissue in the implant, butalso areas which should not be heated and softened, because they aresituated between the heat source and the target area in the plasticmaterial. The subsequent removal of the cooled-off thermoplasticmaterial is difficult and hardly feasible without an excessivewarming-up of the surrounding tissue. These disadvantages are alsopresent at an irradiation with an electromagnetic radiation, forinstance infrared light.

In case of a liquefying with a directly applied ultrasound energy, theproblems mentioned above in connection with an external heat source areactually not present, but the grave disadvantage consists of the factthat the bone must offer a mechanical resistivity sufficient to softenthe (vibrating) thermoplastic material at the contact zone with thebone, and that there is a risk of mechanically damaging the bone. Inprinciple, a bone structure of the greatest possible density must beavailable in order to guarantee a safe fusing-on of the thermoplasticmaterial. At the very point where a good fusing-on of the polymer in thebone would be desirable, especially in the zone of an osteoporotic bone,the fusion of the polymer can only be achieved in an unreliable manner,and in the case of a missing fusion no mechanical connection occurs. Afurther disadvantage of the ultrasound technique is the fact that afterthe polymer's hardening following a completed connection with the bone aliquefying is no longer possible, meaning that the implant cannot beremoved again without major effort (drilling open, tearing out, fusing,and awaiting degradation).

This is where the invention will provide a remedy. The task underlyingthe invention is to create a medical implant capable of being softenedby developing internal heat. The risk of damaging the tissue throughexcessive heat (mostly explained in the following on an example inbones) is reduced, especially in comparison to the state of the art,which uses an en external heat source. The fixation result's dependenceon the quality of the bones is considerably reduced. The electricallyconductive polymer can be re-softened by using electrical current, andat least partially be removed.

The hazards in employing the medical implant according to the inventionare reduced because the actual evolution of heat (to soften the polymer)is generated inside the implant and in the transition between theimplant and the. The release of energy by the current, at the pointwhere the implant contacts the bone, is concentrated inside the implant,and because of the relatively smaller functional cross-sectional surfaceof the conductive implant, the greatest evolution of heat, at greatestcurrent density, occurs at that point (ideally at the contact point).This effect can be further reinforced by a suitable design of theimplant and of the electrode. It has also been demonstrated that afterfusing, a polymer of proper composition can reduce its electricalresistivity up to a factor of 10³-10⁸, and therefore cannotsignificantly be heated further by the flowing current. To a certaindegree the system is therefore self-regulating, and spares thesurrounding tissue. In other embodiments, a correspondingly increasedresistivity has under certain circumstances likewise proved advantageous(for instance for the fusing of polymer particles with each other).

The bone can further be protected by choosing a conductivity of theimplant or of the transition from the implant to the bone which is lowerthan that of the bone, so that the latter warms-up less. If necessarythe bone can also selectively be cooled off by using cooling elements,rinsing fluids or gas/air flows.

The medical implant according to the invention can be realized invarious implant forms, in particular as a screw, pin, clip, prong,plate, nail, spiking wire, cage, pedicle screw (or nail), piercing, skinattachment, medicament carrier, gene material carrier, bioactive factorcarrier (for instance growth factors, bone formation promotingsubstances, pain killers, etc.), as carriers of other implants, as adowel, clamp, pearl, dental implant, dental root implant, hose, tube,thread, thread in a hose or tube, tissue, web, skeleton, stocking, band,loose fibers, fibrous knot, fibrous flocks, granulate, chain, and anchorwith or without a threading eyelet. After the implantation, the implantcan also serve in or on the body for diagnostic, stimulation ormonitoring purposes. The same elements can also be heated by anincorporated wire, a pin or other current carrier (made of the same orof another material, for instance metal), which serve as temporarycurrent suppliers but not directly for warming-up purposes, and canlater optionally be removed. These current conductive elements can lateralso be left in place and be designed conformed to be biologicallyresorbable (for instance, made of magnesium).

The invention solves the intended task by using a medical implant whichexhibits the characteristics according to claim 1, by using a device forfixating bones or bone fragments presenting the characteristics ofpatent claim 70, an osteosynthesis process according to patent claim 71,and a further osteosynthesis process according patent claim 81.

The medical implant according to the invention utilizes the effect thatunder a flowing current, a heat is generated in the electricalconductors or at the transition between electrical conductors at thepoint of the largest (for instance ohmic) resistivity (in a currentcircuit). The specific characteristic of the medical implant accordingto the invention is that an electrical current is used for warming-up apolymer, preferably a thermoplastic material that is electricallyconductive in itself, or can be made electrically conductive byadditives. With the aid of such a thermoplastic, electrically conductivepolymer it is surprisingly possible, through a softening of thethermoplastic material and a suitable implant design and preferablyduring a surgical operation, to achieve mechanical connections on,toward and with human or animal bones. Because of the fact that thegreatest evolution of heat occurs at the point of the greatestresistivity in a current circuit and therefore the greatest voltagedrop, it is also possible to specifically control the warming process sothat the material softens up only at certain preferred points. It shouldbe observed that the current tries to find the path of leastresistivity, this forming a current circuit. The location of greatestresistivity corresponds to the location of the greatest resistivity insuch a current circuit, and the implant is to be designed in a mannersuch as to force the current to flow through desired regions of theimplant, without draining away in other directions. The implant materialacts for the rest as a partial insulator, is crossed by little currentand correspondingly little softened. The human and animal body, and inthis context especially the bone, has proved to be a very suitableelectrical conductor for acting as an onward transmitter of theelectrical current circuit, and in the specific application describedhere warms-up surprisingly little. This is additionally favored by usingpolymers which are reducing their resistivity in a fused condition.

In a particular application, the implant can thus be connected to onepole (in case of a direct current) or to one phase conductor (in case ofalternate current, radio frequency current) of the current circuit,while applying the other pole or zero conductor to the body through alarge surface-area electrode. The current flows over one electrode tothe implant, through the implant and the contact area or point with thebody, for instance the bone in the same, onward through the same andthen exits again through a neutral electrode. The current will warm-upand soften the implant at the desired location of greatest electrical(ohmic, inductive, capacitive or other) resistivity or voltage drop inthe current circuit.

Alternatively the current can also, without crossing the patient's body,be made to pass through the implant between two suitably applied poles(in a “bipolar” manner), so as to again warm up, soften or fuse theimplant at the point or region of greatest resistivity.

The following definitions apply to the following terms frequentlyemployed in the entire description:

Energy: For the warming-up and softening of the implant the inventionutilizes the current flowing through the implant, as suitably applied byelectrodes. The current may be an ohmic current, wherein electrons areflowing in a metal like as under direct current. Protons or other loadedparticles can also be considered as carriers of charges to be moved.However, the current may also be of an ion-shifting type, such as occurswhen a current flows through a saline solution. Chemical reactionscapable of allowing a shifting of electrons or charges like in a batteryare also possible. In particular, this also includes an inductive orcapacitive current, and shifting capacitive charges are the preferredcurrent mode in this application. The current may also be flowing indiverse ways, for instance in bones as an ion current and protoncurrent, in a polymer for instance at the same time as an electroncurrent. The current or electrical voltage may be employed as a directcurrent, alternating current or, preferably, as a high frequencyalternating current (radio frequency). Even a sparking can be used forthe application according to the invention.

Fusing/softening/plasticizing: The terms of fusing, softening orplasticizing of the implant material in the sense of the Invention areintended to mean the softening of the implant by the current flow initself or by the heat generated by the same, until the implant, whichcould previously not be plastically deformed in the body in a usefulmanner (typically by hand), can be allowed to deform by applying amoderate force (typically by hand) and to be used according to theinvention.

Resistivity and conductivity: The terms “electrical resistivity” or“conductivity” are, for the respective type of current used, taken tomean the surface resistivity (Ohm/square), the volume conductivity(S/cm) or the absolute resistivity. These definitions areinterchangeable and not to be understood in a limiting manner. Theinvention aims in particular at an adequate conductivity of thematerial, so as to achieve a sufficient flow of current for thenecessary softening, a certain resistivity is otherwise needed toachieve an adequately large voltage drop and consequently a sufficientlylarge release of energy in the implant to soften the same. It is ideallydesirable to strive for a markedly lower conductivity than in thesurrounding tissue, so as to spare the latter (low warming there).Finally, the conductivity is a function of the current type, voltage,material cross section and volume conductivity/resistivity of thematerial itself, and must be adjusted for the relative application. Inthe complex alternating current calculation, the concept “resistivity”is replaced by a complex entity, the so-called “impedance” with itscomponents “resistivity R” and reactance X”.

Neutral electrode: In case of an alternating current, the term “neutralelectrode” is taken to mean the pole connected with the neutralconductor or grounding.

Monopolar: The term “monopolar” is to mean an application wherein thecurrent discharge (through a neutral conductor, “neutral electrode” orgrounding occurs on the skin or elsewhere on the body through a largesurface electrode), and the alternate current is typically fed-inthrough the implant. The poles can also be inverted.

Bipolar: The term “bipolar” Is in this case taken to mean the directinput and output of the current through two electrodes applied in thenext neighborhood of the implant (for example, electrical tweezers withtwo poles). The advantage lies in this case in the fact that the flow ofcurrent through the body can be reduced or avoided.

Organic semiconductors: “Organic semiconductors” represent a group ofconductive polymers, on one hand the group of charge-carrying complexes(“charge transfer complexes”) and on the other hand the polyacetylene,polypyrrole, polyanilin etc. groups and their derivatives. Thesepolymers can always be present in any mixtures or in their pure trans-and cis-forms.

Self-conductive polymer: This is to mean polymers capable of beingconductive without using other additives, which at this pointadditionally includes co-polymers (for instance a co-polymer betweenlactide and pyrrole, which are also electrically conductive.

Polymer made conductive: This is to mean polymers that are fitted withadditives, typically a powder in a micro- or nanometer range,self-conductive polymers, low molecular weight substances or liquidsmade electrically conductive by these additives. To be explicitlyexcluded from this group are polymers that are fitted with othermacroscopic structural elements, namely fibrous mats, endless fibers,wires, threads, needles etc. so that the polymer itself is no longerconductive but only the structural element additionally present in thepolymer, whose warming softens the surrounding polymer.

The medical implant according to the invention allows solving varioustasks, some of which will be described in greater detail, as follows:

Task A: Selective or Global Warming and Softening or Liquefying ofMedical Implants by Using Electrical Currents During their Implantation.

In this case, in the example of straight pin a current circuit isestablished by using an electrode whose one end (on the side turned awayfrom the bone) is connected to an electrically conductive pin, throughthe pin itself, then over the point of contact to the body (for Instancethe bone) and over the body to a neutral electrode. At the point ofcontact between the implant and the bone the voltage drop is greatest(greatest resistivity) and the thermoplastic material warms-up and turnssoft up to a liquid. The core of the pin is conceived so as not to warmup or only partially so, and to remain hard. The pin can then be driveninto a pre-drilled hole that can for instance be undersized, and thewarmed-up, soft and conductive thermoplastic material is pushed into theinterspaces in the bone. After switching off the current, thethermoplastic material cools off and quickly hardens (<1-2 minutes), andthe mechanical connection is thus established.

Task B: Selective or Overall Warming-Up of a Thermoplastic MaterialContaining Implant to Achieve a Deformation During its Implantation.

In this case, a conductive pin on its way is provided with a zonecontaining of higher resistivity and returned inside the currentcircuit. The pin will warm-up in the zone with the greater resistivity.The pin can deform at this point.

Task C: Achieving a Local Fixation of an Implant Comprising a ConductiveThermoplastic Material in the Body.

Through a suitable production process, for instance by injectionmolding, the pin is provided with a residual stress. Thanks to thewarming-up of the entire pin, the thermoplastic material is relaxed andthe pin shortens and increases in diameter, thus leading to a fixationin or on the surrounding tissue.

Task D: Achieving a Local Connection Between Several Implants Comprisinga Conductive Thermoplastic Material by Welding them to Each Other.

This consists of connecting two thermoplastic implant elements, whichcan be separately inserted into the body. This action must guaranteethat the necessary current can flow through both (or several) implantelements to be connected. After inserting the two (or several) implantelements, the current is admitted, the implant elements soften at theirpoint of contact and can be joined by applying pressure. This may alsoallow gluing up a thread in order to forgo a knot, while passing throughthe current directly through the connection point with a bipolar currentsource.

Task E: Lining of Hollow Organs.

The blood vessels, intestines, stomach, bones, urinary tract, bladder,uterus, gall bladder, tubes, vagina, urethra etc. can be lined with amedical implant produced from the implant material described, forinstance in the form of a stent, and be for example mechanicallyaugmented by the same. In this connection, a stent subject to a residualstress can also expand due to warming, or the stent can, in the softenedcondition and while resorting to mechanical pressure, for instance byexpanding a balloon, be deformed.

Task F: Clamping or Enveloping Soft Tissues or Bones

A stomach strip can for Instance be formed from the implant material (asan open ring), made deformable by supplying current and then connectedto a closed ring. A polymer strip can likewise be employed as a formingmaterial.

Task G: Skin Closing

In particular, polymers having a preferably low fusion point can also beglued directly to the skin, for instance for a mechanical skin closingor for instance as an ECG electrode.

Task F: Production of Implants that can be Changed after Inserting intothe Body, by Cutting the Implant Material Apart.

The implant material used and described here can also be employed forthe purpose of producing implants that can be selectively cut apart oropened by using electrical current. In this manner, a thread may forinstance also be cut by an electrical cautery, in particular at greatvoltage or current or preferably with a small but “sharp” electrode.Dented-in or fused-in pins can thus for instance be cut off at the bonesurface or modeled onto the same, until they fit flat on the surface ofthe bone. Medicament carriers can thus be opened to release their activeingredients.

Any kind of current is suitable for the softening or liquefying of themedical implant according to the invention, in particular directcurrent, alternating current, inductive current (microwave), three phasecurrent, multiple phase/multiple pole current, and typical cauterycurrent patterns.

The transmission of current can be realized in various ways, forinstance as a direct transmission of current by using two electrodes(“bipolar”) passing through the thermoplastic material or in a“monopolar” manner through the body, as a transmission of current byusing a capacitive, ohmic or ionic current, and as a transmission ofcurrent by sparking (arching). Suitable current sources are for instancesources such as an electrical cautery, a VAPR (product name, Johnson &Johnson) or a microwave transmitter.

In case of a radio frequency alternating voltage, the preferredfrequency is an alternating voltage of >20 kHz, typically >300 kHz up to3 MHz (radio frequency). Typical average current source: for small pinsor fixation elements (diameter 0.1-5.0 mm): about 0.1-50.0 Watt,preferably 0.5-10.0 Watt. For the fixation of large prostheses or forthe filling of large bone defects 1-2,000 Watt.

The peak power during a single applied pulse may attain 5 kW and more.

Typical electrical voltage: 20 Volt-3,000 Volt, preferably 20-300 Volt.

Typical current intensity: 0.01-100.00 Ampere, preferably 0.05-10.0Ampere.

Alternating current form (radio frequency alternating current):sinusoidal, rectangular, trapezoidal, etc., asymmetrical or symmetrical,pulsed or continuous.

Typical pulsation lengths: 0.1 ms-5.0 ms.

In particular, it is to be taken into account that the current intensitycan be regulated, by measuring the resistivity/impedance of the currentcircuit (Ohm), current flow (Ampere), power output (Watt) or by direct(for instance heat sensors) or indirect (for instance infrared camera)measurement of the heat of the implant or of the surrounding tissue.This allows preventing an excessive warming-up, and provides a carefultreatment of the implant as well as of the tissues or other implants(threads). Electrical cautery means frequently already offer aregulating mechanism than can also be used for this purpose (for aconstant or modulated power output). Another possibility consists ofmeasuring the mechanical resistivity of the implant during thedeformation, and to regulate the electrical power output accordingly. Asan additional regulating effect it is also possible to employ thepolymer's resistivity change while warming-up or softening, whereby thewarming-up can be controlled (see above in the text).

The biologically compatible and biodegradable polymers for the medicalimplant according to the invention can be chosen from the followinggroup: poly-alpha-hydroxyester, polyorthoester, polyanhydride,polyphosphazines, poly(propylenefumarate), polyesteramide,polyethylenefumarate, polylactide, polyglycolide, polycaprolactone,trimethylenecarbonate, polydioxanone, polyhydroxybutyrate, as well theircopolymers and mixtures.

The biologically compatible, non-biodegradable thermally plasticpolymers for the medical implant according to the invention can bechosen from the following group: polyethylene, polystyrene, polyester,polypropylene, and polysulfone.

The thermally plastic polymers for the medical implant according to theinvention can for instance be chosen from the following group ofmaterials, while reducing the softening point with additives, dependingon the indications:

Acrylonitrile-butadiene-styrene (ABS), polyacryle, celluloide, celluloseacetate, etylenevinyl acetate (EVA), ethylenevinyl alcohol (EVAL),fluoroplastic, ionomere, polyacrylate, polyacrylonitrile, (PAN oracrylonitrile), polyamide (PA or Nylon), polyamidimide (PAI),polyaryletherketone (PAEK or ketone), polybutadiene (PBD), polybutylene(PB), polybutylene terephtalate (PBT), polyethylene terephtalate (PET),polycyclohexylene dimethyleneterephtalate (PCT), polycarbonate (PC),polyketone (PK), polyester, polyethylene (PE), polyetheretherketone(PEEK), polyetherimide (PMP), polyphenyleneoxide (PPO),polyphenylenesulfide (PPS), polyphtalamide (PPA), polypropylene (PP),polyurethane (PUR), polysulfone (PSU), and polyhydroxy ethylmethacrylate(PHEMA).

The desired thermal stability of individual zones of the medical implantcan be varied by the choice of the materials depending on theconductivity, point of fusion as well as specific electrical resistivityof the individual materials.

If the thermoplastic material intended or the medical implant accordingto the invention is in itself not conductive at all points, it can bemodified, by incorporating suitable electrically conductive elements(for instance cables, electrical conductors, cores made of steel ortitanium) at least partially into an electrically conductivethermoplastic material, and thus be designed as a current supplyingelectrode. In this connection the zone of contact to come intoelectrical contact with the patient's body can be coated with thethermally conductive thermoplastic material wholly or partially. If thecontact zone is coated with a conductive thermoplastic material onlypartially, then the remaining surface should preferably not beelectrically conductive. This can be done by appropriately choosing thematerial or by an appropriate coating, such as for instance withhydroxyapatite or other, for instance osteoconductive, osteoinductive orosteogenic materials.

The process steps used in applying a medical implant according to theinvention are now described in closer detail:

-   -   a) Preparation of the bone, for instance by inserting a        borehole;    -   b) Setting the fixation element into the borehole;    -   c) Warming-up the (thermoplastic) implant polymer;    -   d) Pressing the implant into the tissue to be fixated; and    -   e) Allowing the implant to cool and solidify, which can be        assisted for instance by active cooling.

In a preferred form of embodiment the polymer is chosen so that thesoftening occurs below a warming-up temperature of 250° C.

In another form of embodiment the softening occurs below a warming-uptemperature of 150° C., preferably below 100° C. The advantage of thisform of embodiment lies in the fact that it allows an implantation intothe (human or animal) body that is sparing the tissues.

In a further form of embodiment, no structural elements other than thepolymer itself are provided for the warming-up of the implant. This formof embodiment is distinguished by the increased simplicity offabricating and applying the implant.

In another form of embodiment the medical implant comprises means forthe fastening of an electrode.

In yet another form of embodiment the means consist of a recess or anelevation on the surface of the polymer.

In a further form of embodiment the means consist of a material with anelectrical resistivity ρ_(M)<ρ. The advantage of this form of embodimentlies in the fact that the electrical current is preferably flowingthrough the polymer and not though the means used for fastening theelectrodes, thus preventing the latter from fusing with the rest.

In another form of embodiment the polymer is a semiconductor, preferablyan organic semiconductor.

In one more form of embodiment the polymer comprises molecular chainswith extensively conjugated double bonds.

In a further form of embodiment the specific electrical resistivity ρ isgreater than 500 Ohm-cm, preferably greater than 1,500 Ohm-cm.

In another form of embodiment the specific electrical resistivity ρ isgreater than 3,000 Ohm-cm, preferably greater than 10,000 Ohm-cm.

In a further form of embodiment the polymer has a specific surfaceresistivity of at least 10⁻¹ Ohm/square, preferably at least 10²Ohm/square.

In another form of embodiment the polymer has a specific surfaceresistivity of at most 10¹² Ohm/square, preferably of at most 10⁷Ohm/square.

In one more form of embodiment the polymer has a volume conductivity ofat least 10¹¹ S/m, preferably of at least 10⁴ S/m.

In another form of embodiment the polymer has a volume conductivity ofat most 10¹ S/m, preferably of at most 100 S/m. The volume conductivityis typically at most 0.1 S/m.

In a further form of embodiment the electrical resistivity in theimplant is reduced by the fusion of the polymer or the warming-up of theimplant.

In an additional form of embodiment the electrical resistivity in afused or warmed-up condition of the implant is reduced by at least afactor of 0.5, preferably by a factor of 10.

In an additional form of embodiment the electrical resistivity in afused or warmed-up condition of the implant is reduced by a factorof >100. The advantage of this form of embodiment lies in the fact thatthe areas already fused in this manner are no longer warming-up and arethus sparing the surrounding tissue.

In a further form of embodiment the electrical resistivity in theimplant is increased by a fusing of the polymer or a warming-up of theimplant.

In one more form of embodiment the electrical resistivity in a fused orwarmed-up condition of the implant is increased by a factor of at least0.5, preferably by a factor of 10.

In another form of embodiment the polymer is isotropic.

In another form of embodiment the polymer is anisotropic.

In a further form of embodiment the polymer is a thermoplastic material.

In one more form of embodiment the thermoplastic material is taken fromthe group of polyacetylene, poly(ethylenedioxithiphene),poly(phenylinvinylene), polyarylene, polyspiro-bifluorene, polythiopheneor polypyrrole.

In another form of embodiment the thermoplastic material is chosen fromthe following groups:

-   -   Thermoplastic polymers that are electrically conductive in        themselves;    -   Mixtures of non-electrically conductive (matrix) polymers with        fillers or additives allowing conductivity;    -   Copolymers composed of electrically conductive and electrically        non-conductive polymers;    -   Conductive polymers, wherein the application of electricity or        heat can induce a chemical reaction (for instance a        polymerization) or a physical reaction (for instance a geometric        change);    -   Conductive non-polymers, wherein the application of electricity        or heat can induce a chemical reaction (for instance a        polymerization) or a physical reaction (for instance a geometric        change). Such materials can be of an organic or also non-organic        nature, for instance ceramic, gel, collagene or chemical        substances introduced in the liquid of the paste-like        composition, which hardens again after thermal activation.    -   Combinations of the materials mentioned above.

In another form of embodiment the medical implant also comprises, apartfrom the polymer, implant elements made up of other materials, which arepreferably chosen from the following groups: metals, carbon, ceramic,PEEK, non-thermoplastic polymers preferably chosen from the group of thepolymethylmetacrylates, and/or inorganic materials such as calciumphosphate, calcium sulphate or bone cement.

In another form the polymer is electrically conductive in itself.

In one more form of embodiment the electrical conductivity of thepolymer is achieved by an appropriate doping.

In a further form of embodiment the polymer is combined with anelectrically conductive ceramic, in particular one having a glass-likeor amorphous structure.

In still another form of embodiment the polymer is obtained from anon-conductive polymer by using electrically conductive additives.Suitable additives are for instance: particles of soot (“carbon black”),preferably 3-50%; coal fibers of a length of at most 1 mm, preferably3-50%, with the most homogeneous possible distribution in the polymer;coal nanotubes, preferably 0.1-5%; metal particles, especially of iron,titanium, gold, magnesium, steel; salts, especially NaCl, barium,magnesium salts; proteins, bone material; oils; silicates. Allconductive additives can be added in the form of spheres, flocs etc.

In another form of embodiment the electrically conductive additivesconsist of any possible, electrically conductive solid or liquidmaterial in the form of particles, granules, and particle accumulationsof any external shape.

In a further form of embodiment the electrically conductive additivesare chosen from the following materials:

-   -   Metallic materials, for instance iron, magnesium, gold, silver,        alloys or amalgams;    -   Carbon particles, for instance soot, carbon nanotubes,        Fullerene;    -   Salts or substances capable of quickly attracting water, so as        to allow the flow of electricity in the necessary amount. Such        salts may for instance consist of sodium chloride, sodium        sulphate or magnesium salts.    -   Electrically conductive polymers, for instance polymers chosen        from the pyrrole, aniline, dialkylfluorine, thiophene or        ethylenedioxythiophene groups.    -   Biocompatible oils, for instance silicones;    -   Aqueous solutions, preferably saline solutions.

The quantity of fillers/additives must be adapted to the intended usage,so as to adapt the electrical conductivity to the desired purpose, forinstance to adapt the material's electrical resistivity so that thewarmed-up material becomes thermoplastic, capable of flowing or evenliquid, or that the material hardens upon priming a certain chemicalreaction.

In an additional form of embodiment the polymer presents an open-porestructure.

The advantage of this form of embodiment lies in the fact that it favorsthe healing of bones and that it allows electrically conductive liquids,gels or other materials to be held in place.

In one more form of embodiment the polymer presents capillary channels.This makes it possible to achieve the advantage that it allows thepenetration of saline solutions from the body or other liquids, so as tomodulate the conductivity

In another form of embodiment the medical implant consists of ahomogeneous material.

In a further form of embodiment the homogeneous material does notpossess an inner structure.

In one more form of embodiment the polymer is present in the form of animplant coating.

In an additional form of embodiment only a portion of the implant'ssurface is coated with the polymer.

In a further form of embodiment the polymer comprises areas having adifferent specific electrical resistivity ρ, especially in the form ofsurface coatings.

In another form of embodiment the coatings present a variable coatingthickness.

In one more form of embodiment the entire implant or only the polymer ispartially coated with electrically non-conductive materials. This makesit possible to achieve the advantage that this execution of the coatingallows defining a path for the passage of the current. Thecon-conductive coating should serve as an insulation and prevent a shortcircuit.

In another form of embodiment the electrically non-conductive materialpresents osteoconductive, osteoinductive or osteogenic properties.

In a further form of embodiment the electrically non-conductive materialis a polyactide or hydroxyapatite.

In another form of embodiment the polymer comprises a mixture of atleast two electrically conductive thermoplastic materials compatiblewith the body. This form of embodiment is distinguished by areas havingvarious conductivities at a constant implant form. The electricallyconductive thermoplastic material may be present in the form of apolymer, gel, paste or wax.

In one more form of embodiment the medical implant presents a solidform. The advantage of this form of embodiment lies in the fact that anexternal force can be applied on the implant in a better manner.

In a further form of embodiment the polymer is present in a granulatedform. This makes it possible to achieve the advantage that the polymercan be filled into the interspaces, gaps or hollows in this manner, andbe hardened there.

In another form of embodiment the medical implant is produced fromfibers, where the polymer preferably serves as a coating for the fibers.The fibers can be braided, woven or twined and be present as individualthreads, as a net, cloth or bag. The advantage of this form ofembodiment lies in the fact that the textile/fibrous implant can thus beturned into the desired shape and then hardened or glued under the flowof current.

In a further form of embodiment the medical implant Is present as anopen-pore foam or sponge.

In another form of embodiment the medical implant is conformed as a bonefixating element, preferably in the form of a bone screw, bone rod, bonedowel, pin, plate, dowel, hose (tube), thread, thread in a hose/tube oranchor (with a threading eyelet).

In an additional form of embodiment the polymer is conformed as a barand presents a longitudinal central hole, which is useful for alongitudinally sliding reception of a metallic rod connectible to anelectrode, or of a rod firmly connected to an electrode.

In another form of embodiment the medical implant comprises a metal pinor a metal wire receivable in a longitudinal hole, which is fitted withan Insulation except in a partial section at the ends.

In a further form of embodiment the polymer is conformed as a bar andcomprises a peripheral, electrically non-conductive insulating layer.

In a further form of embodiment the polymer is conformed as a bar andcomprises an outer bushing made of a second, conductive polymer with ahigher resistivity.

In another form of embodiment the polymer is conformed as a pearl andreleasably connectible with an electrode in the form of a wire.

In one more form of embodiment the medical implant is conformed as adental Implant or dental root implant.

In a further form of embodiment the polymer is at least partiallypresent in a softened condition.

In an additional form of embodiment the softened condition is generatedby a current passing through the polymer.

In one further form of embodiment the electrical current is generated byan external source of current.

In another form of embodiment the source of current is a source ofalternating current.

In one more form of embodiment the polymer can be warmed-up and softenedby an alternating current with a frequency v higher than 20,000 Hz,preferably higher than 300,000 Hz.

In another form of embodiment the polymer can be warmed up and softenedby an alternating current of a current intensity I between 0.001 and 10Ampere.

In another form of embodiment the polymer can be warmed up and softenedby an alternating current of a voltage U between 20 and 300 Volt.

In another form of embodiment the polymer with a volume V can bewarmed-up and softened to be softened by an alternating current with apower density P=0.005-5 Watt/mm³ within 0.1-10 seconds. The energy thusapplied corresponds to E=0.0005-50 Watt*seconds/mm³.

In one more form of embodiment the polymer does not present a uniformconductivity, and the latter is preferably smaller on the surface of theimplant than in the interior of the implant. In both forms of embodiment(bipolar and monopolar) the implant according to the invention can tothe outside present areas of electrical insulation, meaning that in apin used in a monopolar manner the electrically conductive shaft can forinstance be insulated by a non-conductive layer, and that for instanceonly the tip of the implant can be in electrical contact with the body.It is thus possible to achieve that the implant softens up for instancefirst at the tip and can thus be fused into the bone, while the shaft ofthe pin maintains its stability. This allows achieving the advantagethat a selective warming-up of the polymer is possible, meaningprecisely at the point where it is expected to fuse, liquefy or softendue to the flow of current, preferably at the surface of the implantthat is in contact with the patient's tissue.

In another form of embodiment the electrically conductive polymer of themedical implant does not comprise any internal structural elements,structures or fibers that are impacted from the outside by electricalenergy and are thus warmed-up by the same.

In one more form of embodiment, the generation of heat occurs in anelectrically conductive polymer of the medical implant only by a currentflowing through the electrically conductive polymer.

In an additional form of embodiment, the entire electrically conductivepolymer of the medical implant is crossed by a flow of current, so thata homogeneous warming-up of the same takes place.

In a further form of embodiment the entire electrically conductivepolymer of the medical implant is crossed by a flow of current, so thata non-homogeneous warming-up of the same takes place.

In a preferred form of embodiment of the process the patient's body isin itself used as a neutral electrode of the current circuit.

In another form of embodiment of the process the medical implant isswitched into the current circuit between two bones. This is suitablefor a bone-thermoplastic material-bone application of the medicalimplant.

In one other form of embodiment of the process one electrode of thecurrent circuit is connected with a bone fragment and the secondelectrode with the associated bone or otherwise with the patient's body.

In another form of embodiment of the process, one electrode of thecurrent circuit is connected to the bone fragment and the secondelectrode to the medical implant inserted between the bone fragment andthe bone.

In another form of embodiment of the process the implantation locationis a borehole in a bone.

In a further form of embodiment of the process, the medical implant is,in a non-softened condition, oversized with respect to the borehole inthe bone.

In a further form of embodiment of the process, the medical implant is,in a non-softened condition, not oversized with respect to the boreholein the bone and has an internal residual stress. The application of aresidual stress can for instance occur during the fabrication process,for instance by injection molding.

In another form of embodiment of the process, the electricallyconductive polymer is inserted through an insulated cavity of an implantin the form of a rod, and preferably comprises an electricallyconductive core.

In one more form of embodiment of the process, the electricallyconductive polymer is inserted into a cavity with radially exitingholes.

In a further form of embodiment, the medical implant is employed for aplastic vertebral surgery.

In an additional form of embodiment of the process, the medical implantis employed for the locking and/or centering of implants, in particularfor medullary nails after their inserting into the bone.

In another form of embodiment, the polymer is chosen so that thesoftening occurs above a warming-up temperature of 40° C.

EXAMPLE 1 Plate Osteosynthesis

An resorbable osteosynthesis plate of 1 mm thickness made of apoly-D,L-lactide was applied to the bone fragments to be fixated, andthe necessary holes were drilled into the bone. In this example theplate was fitted with holes for 2.0 mm screws. Holes of 1.7 mm size weredrilled into the bone. An electrically conductive pin of 2.0 mm diameterwas then set up on an electrode connected to a commercially availableelectrical cautery. The pin consisted of poly-D,L-lactide admixed with15 percent of carbon black.

The patient was connected to the neutral electrode of the cautery in aconventional manner. The pin was set up on the pre-drilled hole throughthe screw hole in the plate and subjected to a current (power of 5Watt). The current flowed through the electrically conductive pin andwarmed-up the same. Because the largest electrical voltage drop occurredat the transition from the bone to the pin, the greatest warming-upoccurred here in the pin, whereby the pin was softened up, especially atits surface. By exerting a soft pressure on the electrode, the pin couldthen be pushed into the hole that had been pre-drilled in the bone, andthe thermoplastic material flowed into the accessible inter-trabecularinterspaces in the cancellous bone. After switching off the current, thepolymer cooled off and hardened in less than 1 minute. The pin fittedwith a somewhat oversized head (meaning larger than the borehole in theplate) was now locking the plate at the desired point.

EXAMPLE 2 Plate Osteosynthesis

In a variant of Example 1, a bone plate was used which had likewise beenproduced from the same electrically conductive thermoplastic material asthe pin described above. The pin was inserted as in the above example.As soon as the head of the pin had come in contact with the plate, afusion between the plate and the pin also occurred at this point, as inthe zone of the hole the plate was likewise electrically conductive anda fusion between the plate and the head was achieved at that point.After cooling the pin and the plate were firmly connected to each other,and the connection was thus locked at a stable angle.

EXAMPLE 3 Bone Anchor

The problem to be solved was in this case to fixate a thread in thebone, so as to lock up a tendon or other bone element with a thread. Forthis purpose a hole of a diameter of 3 mm and a depth up to 15 mm wasdrilled into the bone. A thread with a high fusing point was insertedinto the hole in the bone. An anchor of a somewhat greater thicknessthan that of the hole was then set up on the hole. The anchor was madeof polypyrrole having a conductivity of 1,000 Ohm/square.

In a manner similar to Example 1, the anchor was also in this casesubjected to a current by using an electrical cautery, and aftersoftening up by the radiation energy pressed into the bone. Afterswitching off the current, the polymer hardened and the anchor waslocked to the bone, together with the thread.

EXAMPLE 4 Bone Anchor

In a modification of Example 3, the thread was passed through atransversally drilled hole in the anchor, the anchor was then insertedinto the bone and fastened there by using an electrode. The tom-offtendon was then fastened using the thread. The thread was in this caseheld under a traction force. Thanks to the simultaneously switched-oncurrent, the anchor partially fused and was under slight pressure gluedto the thread, thus gaining a hold in the bone. After cooling withinabout 30 seconds, the traction force on the thread could be released. Aknotting of the thread, which would otherwise have been necessary, couldbe omitted.

EXAMPLE 5 Implantation of a Prosthesis

In a dental implant made of titanium, the distal third was surroundedwith a partially conductive thermoplastic material. For this purpose theimplant was several times dipped into a solution of poly-D,L-lactidewith 25% carbon black and dried between the dipping treatments. Forinsulating purposes, the upper two thirds of the surface were similarlycoated with a low molecular weight quick-releasingpolylactide-co-glycolide material.

The side turned away from the root tip was connected to a source ofcurrent. The implant was set up on the hole that had been pre-drilledundersized, and the current was switched on. As soon as the currentflowed through the electrode into the implant, then through the polymerand again through the bone, the coating softened at the distal end, andthe implant could then be pushed deeply into the hole under pressure.The solidification of the polymer in the bone led to a primary,load-resistant connection between the bone and the implant. The coatingmade of polylactide-co-glycolide degrades within a few days and allowsthe bones to grow on the titanium implant thereafter.

EXAMPLE 6 Vascular clip

The clip served to clamp-off blood vessels so as stop bleeding. Itconsisted essentially of two arms and a hinge. The arm was grasped withone clamp and the blood vessel was held locked in the same. The armswere subjected to current and pressed together. The current softened thehinge and allowed a bending of the clip. When the ends of the arms thatwere turned away from the hinge impinged on each other, a current alsoflowed at this point, and induced the fusing and the desired connectingof the two arms.

EXAMPLE 7 Thread Clip

The same application as described in Example 6 could also be employedfor the fixation of threads so as to avoid knots. The clip had a lengthof 7 mm and consisted of two arms of equal length. The cross sectionaldiameter of the arms was 3×3 mm.

EXAMPLE 8 Vertebral Implantation

in a female patient with an osteoporotic compression fracture of thefirst lumbar vertebra, a hole of 4 mm diameter was drilled (under localanesthesia) from dorsal through the pedicles into the vertebral body(length of ab. 4 cm). A pin made of poly-D,L-lactide (of a diameter of3.9 mm) filled with polypyrrole and with a resulting conductivity of1,200 Ohm/square was passed from dorsal and still without anyapplication of current through the hole. The pin itself was externallycoated with a 0.5 mm thick insulating layer made of poly-D,L-lactide anda central longitudinal hole with a diameter of 0.6 mm. This longitudinalhole held a metal rod (of surgical steel) of a 0.5 mm diameter connectedwith the electrode. The electrode was then switched on and the pin waspushed into the vertebral body. Because the pin had no insulation on itstip, it made contact with the bone at that point and fused on the same.When pushing further on the pin (while holding the position of theelectrode in the center, meaning pushing the pin into the depth like athick-walled tube on the electrode) a filling of the vertebral body withthe poly-D,L-lactide could be obtained. While fusing on, the pin wascontinuously losing its insulation at the tip, so that under acontinuous fusing of the material, the pin could be pushed in furtherinto the vertebral body. After a 2-minute cooling, the vertebral bodywas load-resistant and free of pain.

EXAMPLE 9 Electrode Design

This describes a particularly favorable arrangement of implant andelectrode. The electrode is designed so as to be capable, as in Example9, to be moved close to the location where the current is to be applied.In this case, however, the electrode has an insulation and is onlycircumferentially conductive for a length of 7 mm at its tip. In amanner similar to Example 9, the electrode was passed through a hollowpin (made of polylactide with 15% carbon black) and pushed through thepedicle into the vertebral body. The hollow pin could then be pushedover the electrode into the vertebral body with little resistivity.Contrary to the example 8, the pin is in this case not insulated againstthe pedicle wall and nevertheless fuses only at its tip, because theelectrode emits current only at that point. The clinical result is thesame as in Example 8. In an expanded form of embodiment the tip of theelectrode could be equipped with a heat sensor to measure the heatgenerated there and to regulate it with the aid of a regulatingcommutation system at the current source. An excessive evolution of heatcould thus be avoided.

EXAMPLE 10 Defect Filling

The same pin as described in Example 9 was also employed for the fillingof a bone defect, in this case of a tibia head defect. For this purpose,in the patient with the tibia head fracture a 4 mm diameter hole wasdrilled from ventral through the corticalis toward the defect (length of2 cm). The pin was then pushed through this hole into the medullary andthe cancellous space of the bone while applying current, thus creating astable bone as in a composite osteosynthesis. The screws subsequentlyinserted in this area provided an excellent hold in the fused polymer.It has been proven that the subsequent fusing-on of polymer in arecumbent osteosynthesis material or in recumbent prostheses leads tosimilarly stable conditions.

EXAMPLE 11 Composite Osteosynthesis

In the context of a collum femoris fracture in an osteoporosiscondition, a dynamic hip screw was Implanted through the collum femoris,which had been modified as follows: it was internally fitted with anadditional longitudinal borehole of 3 mm diameter, and at the threadedtip with 10 radial holes of 1 mm diameter which allowed a communicationbetween the central borehole and the bone. A pin of 2.9 mm diameterinsulated as in Example 9 was then inserted in this central borehole andsubjected to a current from the rear. Under the effect of the current,the pin could be fused inside the screw, and the liquefied polymerpenetrated through the holes outwardly into the bone, thus creating anaugmentation of the bone wherein the implant locked. After the hardeningof the polymer (2 minutes), the screw was load-resistant.

EXAMPLE 12 Stent

In the context of a vasodilatation, the radiologist inserts a heartcatheter through a femoral access into the femoral vessels, and movesthis catheter to a restricted kidney artery. A balloon with a folded-upstent around it, made of polypyrrole (diameter 1.5 mm, length 2 cm) isapplied to the tip of the catheter. The balloon itself is conductive ina monopolar manner and lies inside the stent in a folded-up state. Theballoon is then subjected to a current and the current flows through thestent to warm-up and soften the same. The balloon can then be blown upand the stent is expanded, until an adequate flow of blood is achieved.The current is switched off and the stent cools off, hardens (within 40seconds) and keeps the vessel open.

EXAMPLE 13 Memory Effect

A bone anchor with an internal residual stress is produced by injectionmolding (PLA/polyaniline). In the now present cooled-off form, theanchor is straight (length 10 mm, diameter 3 mm). While using a threadpassed through an eyelet in the upper third of the anchor, the anchor ispushed under soft pressure into a pre-drilled hole in the outermalleolus. Under the action of heat induced by the mono-polar appliedlight, a relaxation of the anchor is initiated and the same bends over.This causes the anchor to jam in the hole of the bone, and gain amechanical hold there. The thread on the anchor can thus be loaded after30 seconds, and be employed for the reconstruction of a band.

EXAMPLE 14 Nail Locking

A femoral medullary nail is inserted into the femur for anosteosynthesis. However, in this 86-year old female patient the bone wasdistally too soft for a locking operation, the operator thus drilled a 4mm hole from lateral through the corticalis toward the nail. A 3.5 mmpin made of a conductive synthetic material was pushed through the holetoward the nail. The pin was then subjected to a current in a mono-polarmanner and pushed into the medullary canal, whereby it continuouslyfused away from the nail while filling up the medullary canal andembedding the nail. In order to properly distribute the implant materialin the medullary canal, a relatively high level of energy (70 Watt) anda polymer of high thermal capacity were chosen, so as to prevent anexcessively rapid cooling and solidification. After switching off thecurrent, the nail was securely fixated at the center of the femur.

The invention and further developments of the invention will in thefollowing, with the aid of partially simplified drawings of variousexamples of embodiments, be explained in greater detail. These show:

FIG. 1: A longitudinal section through a form of embodiment of themedical implant according to the invention;

FIG. 2 a: A longitudinal section through another form of embodiment ofthe medical implant according to the invention;

FIG. 2 b: A longitudinal section through a further form of embodiment ofthe medical implant according to the invention;

FIG. 3 a: A cross section through another form of embodiment conformedas a dental implant of the medical implant according to the invention,prior to the fusing process;

FIG. 3 b: A cross section through the form of embodiment according toFIG. 3 a, after a completed implantation;

FIG. 4: A longitudinal section through another form of embodimentconformed as a hip joint prosthesis of the medical implant according tothe invention, after a completed implantation;

FIG. 5 a: A view of another form of embodiment of the medical implantaccording to the invention;

FIG. 5 b: A view of the form of embodiment according to FIG. 5 a, aftera completed implantation;

FIG. 6 a: A view of a further form of embodiment of the medical implantaccording to the invention;

FIG. 6 b: A view of the form of embodiment according to FIG. 6 a, aftera completed implantation;

FIG. 7 a: a view of another form of embodiment of the medical implantaccording to the invention;

FIG. 7 b: A view of the form of embodiment according to FIG. 7 a, aftera completed implantation;

FIG. 8 a: A section through another form of embodiment of the medicalimplant according to the invention;

FIG. 8 b: A section through the form of embodiment according to FIG. 8a, after a completed implantation;

FIG. 9 a: A section through another form of embodiment of the medicalimplant according to the invention;

FIG. 9 b: A section through the form of embodiment according to FIG. 9a, after a completed implantation;

FIG. 10: A section through one more form of embodiment of the medicalimplant according to the invention;

FIG. 11 a: A section through another form of embodiment of the medicalimplant according to the invention;

FIG. 11 b: A section through the form of embodiment according to FIG. 11a during the implantation;

FIG. 11 c: A section through the form of embodiment according to FIGS.11 a and 11 b after a completed implantation;

FIG. 12: A section through another form of embodiment of the medicalimplant according to the invention;

FIG. 13: A section through a further form of embodiment of the medicalimplant according to the invention;

FIG. 14: A section through another form of embodiment of the medicalimplant according to the invention;

FIG. 15 a: A section through one more form of embodiment of the medicalimplant according to the invention; and

FIG. 15 b: A section through the form of embodiment according to FIG. 15a after a completed implantation.

In the form of embodiment shown in FIG. 1, the medical implant accordingto the invention comprises a pin 2 with a peripheral insulating layer 1and Is employed for an application in a vertebral plastic surgery(Example 9). A pin 2 made of a blend of polypyrrole and poly-D,L-lactideis inserted, from dorsal through a pre-drilled hole 10 into a pedicle ofa vertebral body 12 to be treated.

The pin 2 itself is externally coated with a 0.5 mm thick insulatinglayer 1 made of poly-D,L-lactide and has a central longitudinal hole 13with a diameter of 0.6 mm. This longitudinal hole 13 holds a metallicpin 14 (made of surgical steel) of a diameter of 0.55 mm, connected withthe electrode 15. After inserting the pin 2, the current is switched onand the pin 2 is pushed, together with its connected electrode 15, intothe vertebral body 12. As the pin 2 does not have an insulation at itstip, it contacts the bone at the point, and fuses on. A further pushingaction on the pin 2 (while holding the position of the electrode 15 inthe center, meaning that the pin 2 is pushed like a thick-walled tubeinto the depth on the electrode 15) can thus achieve a filling 3 of thevertebral body 12 with poly-D,L-lactide. After cooling off for 2minutes, the vertebral body is load-resistant and pain-free. The currentoutflow occurs in a “monopolar” manner through the body of the patientto be treated, over a neutral conductor 18 (neutral electrode orgrounding) on the skin or elsewhere on the patient's body via a largesurface-area electrode, while the alternating current is typically fedin through the medical implant. In another form of embodiment, the pin 2can also be realized without an insulating layer 1, and be pushed inthrough an insulating tube or an insulating hose inserted into the hole10.

The form of embodiment illustrated in FIG. 2 a differs from the form ofembodiment represented in FIG. 1 only by another arrangement of themedical implant and the electrode 15, meaning by a different electrodedesign (Example 10). The electrode 15 is designed so that, like in FIG.1, it can be conveyed close to the location where the current Is to beapplied. At this point, however, the electrode 15 has an insulation 16with low-resistivity and is circumferentially conductive over a lengthof 7 mm only at its tip 17. In a manner similar to the form ofembodiment in FIG. 1, the electrode 15 is inserted into the hollow pin 2(made of polylactide with 15% carbon black) and pushed, together withthe latter, through the pedicle into the vertebral body 12. In contrastto FIG. 1, at this point the pin 2 is not insulated against the pediclewall and nevertheless fuses only at its tip, because the electrode 15transmits current only at that point. In an expanded form of theembodiment (not drawn) the tip 17 of the electrode 15 if fitted with aheat sensor to measure the evolved heat and to regulate it through aregulating commutation at the source of the current. This canadditionally prevent an excessive evolution of heat. The transmission ofcurrent occurs in a “monopolar” manner through the patient's body overthe neutral conductor 18 (neutral electrode or grounding) on the skin 6,while using a large surface-area electrode. An alternative form ofembodiment is represented in FIG. 2 a, which differs from that in FIG. 2a only by the fact that at this point the pin 2 comprises an internalbushing 4 surrounding the electrode 15 and made of a conductive polymerwith a low resistivity, and coaxially an external bushing 5 made of aconductive polymer with a higher resistivity. The external bushing 5 isalso closed at its ending inserted into the vertebral body 12. Based onits higher resistivity, the external bushing 5 warms-up and deformswhile the current flows though the pin 2.

The form of embodiment represented in the FIGS. 3 a and 3 b comprises adental implant 30 made of titanium, whose section to be inserted intothe bone 31 is surrounded by a layer 34 made of a conductivethermoplastic material. For this purpose, the dental implant section 30to be inserted into the bone 31 is repeatedly dipped into a solution ofpoly-D,L-lactide with 25% carbon black and dried between the dippingtreatments. The uncoated end 33 turned away from the distal end 32 isconnected to a source of current. The dental implant 30 is set up on thehole 10 pre-drilled undersize, and the current is switched on (FIG. 3a). As soon as the transmission of current occurs through the electrode15, the dental Implant 30, the layer 34 formed of a polymer and the bone31, the layer 34 softens beginning from the distal end 32, and thedental implant 30 can then be pushed into the depth of the hole 10 underpressure. While pressing the dental implant 30 into the hole 10, thethermoplastic material forming the layer 34 is pressed into theinterspaces in the bone 31, so as to generate a mechanical connectionbetween the dental Implant 30 and the bone 31. The solidification of thepolymer, meaning of the layer 34 in the bone 31, leads to a primary,load-resistant connection between the bone 31 and the dental implant 30(FIG. 3 b).

The form of embodiment represented in FIG. 4 comprises a medical implantconformed as a hip joint prosthesis 50. The hip joint prosthesis 50comprises an electrically conductive metallic femoral component 51,whose shaft 53 to be inserted in the medullary canal 54 of the femur 55is, like in the form of embodiment shown in the FIGS. 3 a and 3 b,coated with a layer 34 made of a conductive polymer, and an equallyconductive metallic articular cup 52 which is, at its outer surfacecontacting the glenoid cavity, coated with a layer 34 made of aconductive polymer. The femoral component 51 is at its uncoated neck 56or its articular head 57 connected to a current source 25′. Thearticular cup 52 is connected to a second current source 25″ in asimilar manner. The femoral component 51 in inserted into the medullarycanal 54 pre-drilled with an undersized hole, and the articular cup 52is inserted in the glenoid cavity. As soon as the current is switched onand the transmission of current takes place across the electrode 15, thefemoral component 51, the layer 34 made of a polymer and the femur 55,the layer 34 softens due to an internal evolution of heat. In the secondcurrent circuit, the transmission of current occurs over a secondelectrode 15, the articular cup 52 and the hip bone, whereby the layer34 on the outside of the articular cup 52 softens due to the internalevolution of heat. The femoral component 51 can now be pushed into thedepth of the medullary canal 54 under pressure. When pressing thefemoral component 51 into the medullary canal 54, the thermoplasticmaterial forming the layer 34 is pressed into the interspaces in thebone, so that a mechanical connection is generated between the femoralcomponent 51 and the bone. In a similar manner the articular cup 52 ispushed into the glenoid cavity, whereby the softened layer 34 on thearticular cup 52 is pressed into the interspaces in the bone, and amechanical connection is likewise generated between the articular cup 52and the bone. The solidification of the polymer, meaning of the layers34 on the femoral component 51 in the femur 55 and on the articular cup52 in the glenoid cavity, leads to a primary, load-resistant connectionbetween the bone and the hip joint prosthesis 50.

The FIGS. 5 a and 5 b show a further form of embodiment, where the pin 2is, through an appropriate production process such as for instanceinjection molding, provided with a residual stress and presents a lengthL and a diameter D in a cooled-down condition (FIG. 5 a). Thanks to thewarming-up of the entire pin 2 through a flow of current between thepoles A, B, the thermoplastic material relaxes and the pin 2 shortensand increases in diameter (FIG. 5 b), which leads a fixation in or onthe surrounding tissue.

In the form of embodiment illustrated in the FIGS. 6 a and 6 b, themedical implant is conformed as a clip 60. The clip 60 is conformed to aU-shape and comprises two arms 61, 62, whose free ends 63 each comprisean element 64 made of a conductive polymer. These elements 64, which arethicker than the arms 61, 62, are connected through electrodes 15′, 15″to a current circuit (FIG. 6 a). After switching on the current source,the clip 60 is pressed together, meaning that the two elements 64 arepressed together. Thanks to the current flow, the two elements 64 arewarmed-up and soften at the contact points which are leaning together,and can thus be joined by applying pressure and fusing them together(FIG. 6 b).

The clip 70 shown in the FIGS. 7 a and 7 b differs from the clip shownin the FIGS. 6 a and 6 b only by the fact that the clip 70 is producedfrom a single piece of conductive polymer. The arms 71, 72 are graspedwith a clamp 74, subjected to current through a respective electrode15′, 15″ and pressed together. Thanks to the current flow, the hinge 73connecting the arms 71, 72 softens and allows a bending of the clip 70.When the ends of the arms 71, 72 turned away from the hinge 73 areimpinging on each other, current is also transmitted at this point,which leads to a fusing and the desired connecting of the two arms 71,72 at their ends which are thickened with respect to the arms 71, 72.

In the form of embodiment illustrated in the FIGS. 8 a and 8 b, themedical implant comprises a thread 80 consisting of a material with ahigh point of fusion and an anchor 83 made of a conductive polymer. Thethread 80 is to be fixated to the bone 81 so that the thread 80 locksfor instance a tendon or another bone element. For this purpose, a hole82 having a diameter of 3 mm Is drilled to a depth of 15 mm into thebone 81. The thread 80 is then inserted in this hole 82 in the bone 81.An anchor 83 having a slightly greater diameter than the hole 82 is thenset up on the hole 82. In a manner similar to Example 1, the anchor 83is also subjected to current through an electrical cautery, and afterbeing softened by the flow of current, pressed into the bone 81. Afterswitching off the current, the conductive polymer solidifies and theanchor 83, together with the thread 80, is fixated in the bone 81.

The form of embodiment shown in the FIGS. 9 a, 9 b is suitable for thefilling of defects in the bone 94. In a manner similar to the form ofembodiment according to FIG. 1, a pin 2 is used which has a central,enclosed hollow space 91 at the tip of pin 2 to receive a metallic pin14 connected with an electrode 15. The metal pin 14 can be removed againafter the pin 2 has fused, or can also be produced from a resorbablematerial. In order, for instance, to fill a tibia head defect in apatient affected by a tibia head fracture, a hole 95 with a diameter of4 mm is drilled from ventral, through the corticalis, up to the defect(length of 2 cm). The pin 2, together with the metallic pin 14, is thenpushed through this hole 95 into the medullary canal and into thecancellous space of the bone while applying a current and thus creating,as in a composite osteosynthesis, a stable bone by a fusing of the pin 2to a filling 93. The screws (not shown here) subsequently inserted intothis filling 93 provide an excellent hold in the initially fused andthen hardened polymer material.

FIG. 10 illustrates a form of embodiment wherein the polymer of themedical implant is conformed as a pearl 102. This pearl 102 can beinserted into the hollow space that arises when a bone fragment 101 isbroken out of a bone 103. The fitting of the bone fragment 101 into thehollow space and the connecting of the bone fragment 101 with the bone103 by fusing the pearl 102 and pressing the polymer into theinterspaces in the bone fragment 101 and the bone 103 can be achievedthrough two variants A and B. In the variant A, a first electrode 15′ isconnected to the pearl 102, while a second electrode 15″ fastened to thebone fragment 101. After switching on the current source, thetransmission of current takes place from the current source over thefirst electrode 15′ and the pearl 102 while warming it up and over thesecond electrode 15″. In the variant B the first electrode 15′ isfastened to the bone fragment 101, while the second electrode 15″ isfastened to the bone 103. At this point, after switching on the currentsource the transmission of current occurs over the first electrode 15′,the bone fragment 101, the pearl 102 while warming it up, the bone 103and the second electrode 15″.

The form of embodiment shown in the FIG. 11 a-11 c comprises a pin 2made of a conductive polymer suitable for fixating a bone plate 110 on abone 111. The bone plate 110 is a resorbable osteosynthesis plate with athickness of 1 mm, made of a poly-D,L-lactide. In order to fixate thefracture, the bone plate 110 is applied to the bone fragments to befixated, and the holes 112 needed for its fixating to the bone 111 aredrilled into the bone 111. This example shows a bone plate 110 fittedwith screw holes 113 for 2 mm screws. The holes 112 drilled into thebone 111 have a diameter of 1.5 mm. The electrically conductive pin 2 isconveyed with its tip 114 to be inserted into the bone 111 through thescrew hole 113 in the bone plate 110, set up on the hole 112 which hasbeen pre-drilled into the bone 11, and subjected to a current. Thetransmission of current through the electrically conductive pin 2warms-up the same. Because the largest electrical voltage drop occurs atthe transition between the bone 111 and the pin 2, the greatest heatarises at this point in pin 2, which softens up the pin 2, especially atits surface. By exerting a pressure on the electrode 15, the pin 2 ispushed Into the hole 112 which has been pre-drilled into the bone 111,and the thermoplastic material flows into the available intra-trabecularinterspaces in the cancellous bone (FIG. 11 b). After switching off thecurrent the polymer cools off again and solidifies. The head 115 of thepin 2, which has a diameter larger than the screw hole 113 in the boneplate, now locks the bone plate 110 (FIG. 11 c).

The FIGS. 12 and 13 each show a pin 2 which comprises a core 121, 131,made of a material of low resistivity, for instance of a metal or of aconductive polymer and a coating 122, 132 made of an electricallyconductive polymer with a higher resistivity. The coating 122 in FIG. 10is conformed like a bushing and extends over the cylindrical portion 123of the pin 2. The tip 124 of the pin 2 and the axially opposite rear end125, which can be connected to an electrode, are conformed without acoating 122. The coating 132 in FIG. 13 is only partially applied on afrontal section 133 of the pin 2, and encloses the tapering section 133of the pin 2 including its tip 134. A pin 2 conformed according to theFIG. 12 or 13 allows a selective warming up of a thermoplastic material,so as to achieve a deformation. In FIG. 12 the pin 2 will warm-up at thethin tip 124, because the bushing acts as an insulator and the currentflows out through the tip. In FIG. 13 the pin 2 will warm up and deformat the zone with a larger resistivity in the current circuit, meaning onthe coating 132.

FIG. 14 shows the application of a pin according to FIG. 12, for thefilling of a defect in a bone 94 as described in the FIGS. 9 a and 9 b.

The FIGS. 15 a and 15 b illustrate a form of embodiment where themedical implant comprises a dynamic hip screw 150 and a pin 2 made of aconductive polymer. The dynamic hip screw 150 has a hollow shaft 151with a threaded borehole 152 on its frontal end extending up to the headof the hip joint. The region of the threaded borehole 152 has radialperforations 153 that radially perforate the shaft 151 between itscentral hollow space 154 and its perimeter. Apart from the perforations153, the hollow space 154 is fitted with an insulating coating 155. Inthe context of a collum femoris fracture, in the presence of anosteoporosis the dynamic hip screw 150 is implanted through the collumfemoris. As described in Example 9, an isolated pin 2 of a diameter of2.9 mm diameter is then inserted into the central hollow space 154, andconnected, through an electrode 15, at its rear end opposite thethreaded borehole 152 of the dynamic hip screw 150, to a current source25. Under the application of current, the pin 2 thus fuses inside thehip screw 150 and the liquefied polymer penetrates through theperforations 153 toward the outside into the bone 156, thus creating anaugmentation of the bone 156 in which the implant locks up. After thesolidification of the polymer, the hip screw 150 is load-resistant (FIG.15 b).

1-84. (canceled)
 85. A method for osteosynthesis comprising:positioning, at an implantation site, a medical implant comprising abiocompatible polymer element being heat-softenable responsive to anelectric current; heating and softening the biocompatible polymerelement of the medical implant by passing an electric currenttherethrough; and introducing the heated and softened biocompatibleelement into the implantation site.
 86. The method of claim 85,comprising using a patient's body as an electrode to supply electriccurrent to the biocompatible polymer element of the medical implant. 87.The method of claim 85, wherein positioning comprises positioningbetween first and second bones.
 88. The method of claim 85, comprisingcoupling a first electrode with a bone fragment and coupling a secondelectrode with a bone to supply the electric current to thebiocompatible polymer element of the medical implant.
 89. The method ofclaim 85, comprising coupling a first electrode to a bone fragment, andcoupling a second electrode with the medical implant inserted betweenthe bone fragment and a bone.
 90. The method of claim 85, wherein theimplantation site comprises a bone bore.
 91. The method of claim 90,wherein the medical implant is oversized in the non-softened statecompared to the bone bore.
 92. The method of claim 90, wherein themedical implant in the non-softened state is not oversized compared tothe bone bore and has an internal pre-stress.
 93. The method of claim85, wherein the biocompatible polymer element is in a form of a barinserted through a hollow space of an implant.
 94. The method of claim85, wherein the biocompatible polymer element is inserted into animplant having a hollow space with radial exit holes.
 95. The method ofclaim 85, wherein the biocompatible polymer element comprises anelectrically conductive polymer.
 96. The method of claim 85, wherein theimplantation site is for vertebroplasty.
 97. The method of claim 85,wherein the medical implant is for intramedullary nailing.
 98. Themethod of claim 85, wherein the biocompatible polymer element has asoftening temperature above 40° C.
 99. A method for osteosynthesiscomprising: positioning, at an implantation site, a bone fixation devicecomprising a bone plate with at least one through hole; positioning amedical implant, which is oversized with respect to the at least onethrough hole, adjacent the at least one through hole, the medicalimplant comprising a biocompatible polymer element being heat-softenableresponsive to an electric current; heating and softening thebiocompatible polymer element of the medical implant by passing anelectric current therethrough; fixing the bone fixation device to a boneby inserting the heated and softened biocompatible element into the atleast one through hole.
 100. The method of claim 99, wherein thebiocompatible polymer element comprises an electrically conductivepolymer.
 101. The method of claim 99, wherein the biocompatible polymerelement has a softening temperature above 40° C.